Semi-occlusive dressings don't foster infections

Studies prove they are safe

By Liza G. Ovington, PhD, CWS

President, Ovington & Associates

Dania, FL

When the concept of semi-occlusive dressings was first introduced, there was a general fear that such dressings, by supporting a moist environment, would lead to increased infection rates because bacteria present in the wound environment would proliferate. This fear persists today, but is largely unfounded.

While semi-occlusive dressings should be used with caution on wounds that are known to be infected, they do not promote infection in and of themselves.

Prospective studies and multiple reviews of the literature have demonstrated that this fear of infection is not borne out. A review of published data from 36 papers discussing infection in 1,085 wounds dressed with conventional materials (including gauze as well as antimicrobial agents such as silver sulfadiazine and chlorhexidine) revealed an overall infection rate of 7.1%. A tandem review of 75 papers discussing infection in 3,047 wounds dressed with semi-occlusive materials (films and hydrocolloids) revealed an overall infection rate of 2.6%, or less than half that of the conventionally dressed wounds.1

Another retrospective review of 103 papers published on occlusive dressings of all types reported an overall infection rate of 5.37% in wounds under conventional dressings and 2.08% in wounds under semi-occlusive dressings - again less than half the rate of conventionally dressed wounds.2

Also, a prospective trial of venous ulcers, burns, and donor sites treated with conventional dressings (impregnated gauze) vs. semi-occlusive (hydrocolloid) dressings demonstrated infection rates of 5.39% and 1.9% respectively.3

Several explanations have been offered to account for these reduced infection rates seen with occlusive dressings. It has been suggested that semi-occlusive dressings enhance the activity of endogenous phagocytic cells that mount a defense against foreign bacteria in the wound by maintaining a moist environment. When the wound is kept moist, neutrophils remain viable and can perform their normal function of removing invading organisms. Neutrophils do not freely penetrate wounds that are allowed to dry out. Semi-occlusive dressings are also able to maintain a mildly acidic wound pH, which is detrimental to bacteria.

It has been shown that a semi-occlusive dressing can serve as an effective physical barrier to exogenous bacteria from the environment,4 whereas up to 64 layers of gauze cannot prevent the entry of bacteria into the wound.5 It also has been suggested that the use of occlusive dressings is associated with reduced airborne dispersal of microorganisms as compared to textile products.5 Removal of conventional cellulose dressings from bacterially colonized wounds liberates wound bacteria into the air, and the numbers are slow to decline. Removal of a hydrocolloid dressing from an experimentally colonized wound resulted in significantly fewer numbers of airborne bacteria.

It is important to distinguish between bacterial contamination, colonization, and infection. Intact skin is always populated by a variety of bacterial species, and any open wound is quickly "contaminated" by these resident bacteria. Contamination in this sense means only that bacteria are present. It is important to remember that not all bacteria are pathogens, and their presence alone does not herald infection.

Colonization of a wound by bacteria is defined as the state that exists when bacteria have become adherent to superficial tissues and have begun to proliferate. Colonization of wounds by bacteria does not necessarily stop the healing process.6 Infection occurs when these adherent, proliferating bacteria then invade healthy tissues, continue to proliferate, overwhelm the body's defenses, and cause toxic effects due to their numbers or excreted toxins. One way to think about infection is to consider it as being defined by an equation that takes into account the type of organism, its amount, and the ability of the host to defend itself7:

(Number of organisms) x (virulence of organism)

resistance of host

Semi-occlusive dressings create a moist wound environment for healing that may appear unfamiliar to patients and clinicians accustomed to dry wounds. Moist wounds also tend to have more noticeable odors than dry wounds, and many of the dressings create gels or leave residues that resemble pus or purulent drainage in the wound. However, if semi-occlusive dressings are used appropriately with aseptic technique, they will not promote wound infection.

The issue of occlusion and infection has been addressed in multiple symposia, including the First International Forum on Wound Microbiology, held in Barcelona, Spain, in 1989. The American Journal of Surgery addressed the subject in a January 1994 supplement titled Wound Infection and Occlusion: Separating Fact from Fiction. The supplement contains 14 papers presented at an international symposium held in London.


1. Hutchinson JJ, McGuckin M. Occlusive dressings: a microbiologic and clinical review. Am J Infect Control 1990; 4:257 -268.

2. Hutchinson JJ. Prevalence of wound infection under occlusive dressings: a collective survey of reported research. Wounds 1989; 1:123-133.

3. Hutchinson JJ. "A Prospective Clinical Trial of Wound Dressings to Investigate the Rate of Infection Under Occlusion." In: Proceedings: Advances in Wound Management. London: MacMillan; 1993, pp. 93-96.

4. Mertz PM, Marshall DA, Eaglstein WH. Occlusive wound dressings to prevent bacterial invasion and wound infection. J Am Acad Dermatol 1985; 4:662-668.

5. Lawrence JC. Dressings and wound infection. Am J Surg 1994; 167(1A):21S-24S.

6. Thomson PD. What is infection? Am J Surg 1994; 167:7S-11S.

7. Mertz P, Ovington L. "Wound Healing Microbiology." In: Dermatologic Clinics Vol. 11. 1993, pp. 739-748.